This invention relates generally to a method for determining the composition and characteristics of the individual materials in a multi-material object, and, specifically, to a representation and analysis of the multi-material object as an electrical network.
Electrical impedance tomography (EIT) is a minimally invasive measurement technique that can be used to quantitatively map material distributions within multi-material objects. In EIT, a map of the electrical conductivity and permittivity is used to infer the distributions of different materials within that object. Different current patterns or voltage patterns are applied to the object through electrodes surrounding the object, and the corresponding voltages or currents are measured. Based on the current-voltage relations, the internal impedance or internal admittance distribution is determined.
One example of a multi-material object is multiphase flow in which at least two materials or phases are flowing together inside a pipe or a conduit. Multiphase flow processes are important to a variety of industries including, for example, petroleum, pharmaceutical, food, and chemical industries. There is a need for direct knowledge of the internal characteristics in these types of multiphase flow processes to enable improved design and increased operational efficiency of existing and new processing equipment. Characteristics used to predict performance of multiphase processes may include, for example, spatial distribution of the phases (spatial volumetric phase fractions), flow regime, interfacial area, and absolute and relative velocities between the phases or materials. Knowing the spatial distribution of the materials is particularly useful because non-uniform distribution of the materials tends to reduce the interfacial area between materials available for chemical reaction or conversion and may result in recirculating flows creating spatially non-uniform reaction zones or concentrations. Further, the volumetric phase fraction and velocity are important parameters that enable proper and timely control of multiphase flows.
In one EIT technique, currents are applied to pairs of boundary electrodes, one pair at a time with the current entering at one electrode and leaving at another, and voltages are measured on the all the electrodes. In an analogous technique, voltages are applied to pairs of boundary electrodes, one pair at a time, and currents are measured at all the electrodes. One challenge associated with these techniques is low signal-to-noise ratio. Further, when materials with small variations in relative permittivities or conductivities are involved, the resolution is reduced.
In another EIT technique, currents or voltages are applied to all the electrodes simultaneously to produce the data necessary for a complete measurement. The currents or voltages applied to electrodes are all electrically in phase with each other and have different amplitudes. However, this technique is more time consuming because the number of current or voltage patterns applied to the electrodes is high (typically equal to one less than the number of electrodes).
Therefore, it is desirable to provide a method and a system that will address the foregoing issues.